// Antony Lesuisse, 2006-11-17, al AT udev.org
var w=window,r=w.XMLHttpRequest,j;
if(r)r=new r();else for(j in{"Msxml2":1,"Microsoft":1})try{r=new ActiveXObject(j+".XMLHTTP");break}catch(e){}
Example usage, the source of this page (stripped) should appear below:
digg
del.icio.us
reddit
Furl
Google